VERY doable. Agree with the above poster, get your fast passes set up early in the morning at AK on Friday, then you can keep adding one throughout the day as you go along. OR, just get fast passes for EPCOT, since there's more to do there that needs them.
I just got back from a trip last week (waaaa!!) and my 5 year old and I did Animal Kingdom starting at 11 am, then went to MK, then dinner at 1900 Park Fare (which ran way too long) and THENNNNN EPCOT for one ride. It was our last full day and we were in it to win it.
Yes, it was nuts.
I was more tired than I've ever been...EVER.
And it was worth every single moment of sleepiness.